Some good postings today from Joe Romm, Climate Central, and others, on the best way to understand how climate change has been affecting extreme weather events.
From Climate Progress – Highly recommended reading:
Climate science suggests that global warming will make hurricanes like Irene more destructive in three ways (all things being equal):
- Sea level rise makes storm surges more destructive.
- “Owing to higher SSTs [sea surface temperatures] from human activities, the increased water vapor in the atmosphere leads to 5 to 10% more rainfall and increases the risk of flooding,” as NCAR Senior Scientist Kevin Trenberth put it in an email to me today.
- “However, because water vapor and higher ocean temperatures help fuel the storm, it is likely to be more intense and bigger as well,” as Trenberth writes
CP’s Joe Romm quotes Jeff Masters:
… this year sea surface temperatures 1 – 3°F warmer than average extend along the East Coast from North Carolina to New York. Waters of at least 26°C extend all the way to Southern New Jersey, which will make it easier for Irene to maintain its strength much farther to the north than a hurricane usually can. During the month of July, ocean temperature off the mid-Atlantic coast (35°N – 40°N, 75°W – 70°W) averaged 2.6°F (1.45°C) above average, the second highest July ocean temperatures since record keeping began over a century ago (the record was 3.8°F above average, set in 2010.) These warm ocean temperatures will also make Irene a much wetter hurricane than is typical, since much more water vapor can evaporate into the air from record-warm ocean surfaces.
To see how warm sea surfaces can affect such a storm, review this vid from 2005 of Katrina. Watch as the storm crosses florida as a category 1, weakens, and then explodes into a Cat 3-5 as it busts out into the then-record warm waters of the Gulf.
The question: is this weather disaster caused by climate change?
Wrong question.
Here’s the right question: is climate change making this storm worse than it would have been otherwise?
Answer: Absolutely
For one thing, sea-surface temperatures in the Atlantic Ocean are higher now than they used to be, thanks to global warming, and ocean heat is what gives hurricanes their power. All other things being equal, a warmer ocean means a more powerful storm. It’s hard to say that all other things are exactly equal here, but it’s certainly plausible that Irene would have been a little weaker if precisely the same storm had come through, say, 50 years ago.
What we know for sure, however is that thanks largely to climate change, sea level is about 13 inches higher in the New York area than it was a century ago. The greatest damage from hurricanes comes not from high winds and torrential rains — although those do cause a lot of damage. It’s from the storm surge, the tsunami-like wall of water a hurricane pushes ahead of it to crash onto the land. It was Hurricane Katrina’s storm surge, not the wind or rain, that destroyed New Orleans back in 2005.
With an extra foot of sea level to start with, in other words, Irene’s storm surge is going to have a head start. And climate change is a big part of the reason why.
1. You say, “What we know for sure, however is that thanks largely to climate change, sea level is about 13 inches higher in the New York area than it was a century ago.” If by “climate change” you actually mean “anthropogenic CO2-driven climate change,” then what you said isn’t even close to true.
The average rate of coastal sea level rise has actually slowed slightly in the last 75 years. Numerous studies have confirmed that fact, and even the alarmist IPCC’s TAR admitted the “observational finding of no acceleration in sea level rise during the 20th century.”
Sea level, as measured by the tide gauge at The Battery, NYC, is rising at 2.77 mm/yr (10.9 inches/century), a rate which hasn’t changed in more than a century; you can see it graphed here:
http://tidesandcurrents.noaa.gov/sltrends/sltrends_station.shtml?stnid=8518750
Because the rate is essentially unchanged from 100 years ago, it is clear that the rise in sea level is not caused by CO2-driven anthropogenic climate change. The current rate of sea level rise preceded significant human contributions to atmospheric CO2.
What’s more, in that area, the land is subsiding. (That’s not surprising: the crust of the earth is a thin layer on top of a big blob of magma, which is SLOSHING.)
According to Peltier’s VM4 GIA model, New York is subsiding at an estimated rate of 0.85 mm/year:
http://www.psmsl.org/train_and_info/geo_signals/gia/peltier/drsl.PSMSL.ICE5G_VM4_L90.txt (see station 960121)
According to Peltier’s GIA VM2, it is subsiding at an estimated rate of 1.64 mm/year:
http://www.psmsl.org/train_and_info/geo_signals/gia/peltier/drsl.PSMSL.ICE5G_VM2_L90.txt
That land movement results in apparent sea level rise which has nothing to do with warming, whether natural or anthropogenic, and it accounts for between 30% and 60% of the 10.9 inches of sea level rise over the last century at New York.
2. There’s no sign that hurricanes and other major weather events are getting larger or more frequent. Note that this is the first hurricane to hit the USA in nearly 3 years, and it went ashore as a mere category 1 storm.